1. Field of the Invention
The present invention relates to image equipment having image forming elements such as an image sensor element or a display element, and also to a vibrating device designed to vibrate the dust-screening member that is arranged at the front of each image forming element of such an image equipment.
2. Description of the Related Art
As image equipment having image forming elements, there is known an image acquisition apparatus that has an image sensor element configured to produce a video signal corresponding to the light applied to its photoelectric conversion surface. Also known is an image projector that has a display element, such as liquid crystal element, which displays an image on a screen. In recent years, image equipment having such image forming elements have been remarkably improved in terms of image quality. If dust adheres to the surface of the image forming element such as the image sensor element or display element or to the surface of the transparent member (optical element) that is positioned in front of the image forming element, the image produced will have shadows of the dust particles. This makes a great problem.
For example, digital cameras of called “lens-exchangeable type” have been put to practical use, each comprising a camera body and a photographic optical system removably attached to the camera body. The lens-exchangeable digital camera is so designed that the user can use various kinds of photographic optical systems, by removing the photographic optical system from the camera body and then attaching any other desirable photographic optical system to the camera body. When the photographic optical system is removed from the camera body, the dust floating in the environment of the camera flows into the camera body, possibly adhering to the surface of the image sensor element or to the surface of the transparent member (optical element), such as a lens, cover glass or the like, that is positioned in front of the image sensor element. The camera body contains various mechanisms, such as a shutter and a diaphragm mechanism. As these mechanisms operate, they produce dust, which may adhere to the surface of the image sensor element as well.
Projectors have been put to practical use, too, each configured to enlarge an image displayed by a display element (e.g., CRT or liquid crystal element) and project the image onto a screen so that the enlarged image may be viewed. In such a projector, too, dust may adhere to the surface of the display element or to the surface of the transparent member (optical element), such as a lens, cover glass or the like, that is positioned in front of the display element, and enlarged shadows of the dust particles may inevitably be projected to the screen.
Various types of mechanisms that remove dust from the surface of the image forming element or the transparent member (optical element) that is positioned in front of the image sensor element, provided in such image equipment have been developed.
For example, U.S. Pat. No. 7,492,408 discloses electronic image acquisition equipment that includes a dust removing mechanism. In the dust removing mechanism, a transparent glass plate shaped like a disc (dust-screening member) is arranged on the front of an image sensor element, forming one unit, and a pair of ring-shaped piezoelectric elements (vibrating members) are secured to the glass plate, each extending along the circumference of the glass plate. A voltage of a prescribed frequency is applied to each piezoelectric element, producing a bending wave that travels in the circumferential direction of the glass plate. Dust is thereby removed from the glass plate shaped like a disc. U.S. Pat. No. 7,492,408 also discloses a method of producing a wave travelling in the circumferential direction of the glass plate. In this method, ring-shaped piezoelectric element is secured and positioned concentric to the glass plate shaped like a disc.
U.S. Pat. No. 7,006,138 discloses a camera that includes a dust-removing mechanism. This dust-removing mechanism has two piezoelectric elements provided, respectively, at two opposite sides of a dust-screening member shaped like a rectangular plate. The piezoelectric elements are vibrated at a prescribed frequency, and causing the dust-screening member to undergo resonation. Thus, the mechanism operates in a vibrational mode, producing a bending wave that travels from one of the sides to the other side, thereby removing dust from the rectangular dust-screening member. In such vibrational mode as disclosed in U.S. Pat. No. 7,006,138, the dust-screening member to which the piezoelectric elements, i.e., vibrating members, are secured vibrates at the same amplitude at its entire surface.